Project Summary MAF1 is a conserved nutrient- and stress-sensitive repressor of gene transcription. Best known for its role as a master regulator of RNA polymerase III transcription in yeast, MAF1 has also been shown to affect the expression of select genes transcribed by RNA polymerase II in mammalian cells. MAF1 repression of RNA polymerase III regulates the synthesis of transfer RNAs, 5S rRNA and other abundant non-coding RNAs that together account for ~15% of total RNA in every cell. Thus, MAF1 function is thought to be important for metabolic economy. Recent dramatic proof of this view was provided by the finding that mice with a whole body knockout of Maf1 are lean and profoundly resistant to diet-induced obesity and non-alcoholic fatty liver disease. Maf1 KO mice are metabolically inefficient, have increased energy expenditure and have an extended lifespan indicative of improved health. The current understanding is that increased RNA pol III transcription in every tissue places such a demand on the energetically expensive synthesis of nucleotides that it alters the balance between energy utilization and storage. Thus, the long term goal of this project is to determine how the absence of MAF1 changes gene expression and metabolism to alter metabolic efficiency and energy expenditure. Aim I of this proposal will examine how gene expression has been altered in key metabolic tissues of Maf1-/- mice by transcriptome and ribosome profiling and by investigating tRNA population effects on translation efficiency and fidelity. Aim II will determine the metabolic changes underlying the increased energy expenditure of Maf1-/- mice by targeted metabolite profiling. These studies will focus on central metabolic pathways and will be complemented by stable isotope measurements of whole body lipolysis and flux through the pentose phosphate pathway, processes that we hypothesize are associated with the enhanced supply and consumption of metabolic energy in the mice. Aim III will investigate the role of RNA pol III transcription in driving energy expenditure in Maf1-/- mice through unrestrained synthesis of highly abundant non-coding RNAs, including transfer RNA and non-specific transcription. Nascent elongating transcript sequencing will locate and quantify RNA pol III molecules genome-wide and a new mouse model will be created to suppress Maf1 KO phenotypes that result directly or indirectly from elevated RNA pol III transcription. Finally, the studies in aim IV will determine whether loss of MAF1 in young and adult mice via inducible and systemic Cre- mediated recombination increases metabolic inefficiency. These experiments are expected to support the concept that the postnatal function of MAF1 is critical for metabolic economy while providing a powerful demonstration of the potential of MAF1 as an anti-obesity drug target.